Self-effacing nozzle for ramjet



M- RAVEL SELF-EFFACING NOZZLE FOR RAMJET May 25, 1965 2 Sheets-Sheet 1 Filed 001?. 30. 1961 7 \QL. "gcgpg May 25, 1965 M. RAVEL 3,184,916

SELF-EFFACING NOZZLE FOR RAMJET Filed 001;. 30, 1961 2 Sheets-Sheet 2 United States Patent 3,184316 SELF-EFFACING NOZZLE FGR RAMJET Maurice Ravel, Morsang-sur-(lrge, France, assignor to Nerd-Aviation Societe Nationale de (Zonstructions Aeronautiques, Paris, France, a joint-stock company of France Filed Get. 30, 1961, Ser. No. 148,426 (liaims priority, application France, Feb. 23, 1961, 853,662 9 Claims. (Cl. 60 35.6)

The present invention concerns a self-eifacing outlet nozzle for a ramjet engine, adapted to facilitate its ignition at high velocities and to enable the starting-up, if desired, of internal air intake feed turbo-pumps.

Ramjet engines propelling missiles can be started either at low velocity during the period when they are accelerated by an auxiliary propulsion unit, or at high velocity after their separation from this propulsion unit.

In the latter case (ignition at high velocity), it is necessary to reduce the velocities of air flow through the propulsion unit to 'allowignition and it is desirable to maintain a high pressure in the cold propulsion unit to prevent any risk of buckling the central body at the moment of starting-up; a self-eifacing outlet nozzle is indispensable and, moreover, the time for effecting such effacement must be extremely short since the thrust of the propulsion unit is low under such conditions.

In the first case (ignition at low velocity), it is necessary to shutter the outlet section when the fuel supply is provided by a turbo-pump whose turbine air intake is positioned within the ramjet, which is the most frequent arrangement.

The object of the present invention is therefore, an outlet nozzle constructed from a material which melts atthe desired temperature and which fulfills the following requirements It is sulficiently strong to withstand stress when the engine is not operated;

When the engine is started it is shed after a preset interval of time which can be of less than one second;

The securing must not, if possible, involve any part attached to the combustion chamber which may be the cause of initiating rupture, or subsequent leakage;

The eifacernent of the outlet must not cause any flameout.

applied along a portion of its length to the inner wall of the normal outlet nozzle and that it comprises a convergent body whose minimum cross-section is less than the minimum cross-section of the normal outlet nozzle and means for fixing the two nozzles together.

The meltable material employed must melt at low temperature. According to a preferred embodiment, this material can be magnesium alloy, an aluminum alloy or a thermoplastic material.

In a preferred form of embodiment, the normal outlet nozzle being convergent-divergent, the means for fixing the two nozzles together comprise a short portion of the self-effacing nozzle applied to the inner wall of the normal outlet nozzle, the walls of the two nozzles in contact with each other being parallel to their common axis, together with associated screws or bolts.

In another preferred form of embodiment, the normal outlet nozzle being convergent-divergent, the means for fixing the two nozzles together comprise a portion of the self-eifacing outlet nozzle applied to the inner wall of the. normal outlet nozzle upstreamof its neck and tensioned springs downstream of said neck between the two nozzles,

said springs being evenly distributed around their common axis.

The springs fixing the two nozzles with respect to each other in this present embodiment can be replaced by rods of adjustable length.

The wall of the self-effacing outlet nozzle can comprise lines of preferential rupture following which the amount of material is reduced in order to decrease the time required for the rupture of heat of the wall after starting up the ramjet engine, said lines of preferential rupture enabling portions to be marked into the wall of the selfetfacing outlet nozzle which will be shed before being melted, the shedding of said nozzle then being able to take place in stages.

These lines of preferential rupture can be embodied by any conventional means, such as grooves, rows of circular or slot-shaped holes which are all identical and uniformly spaced from one another, etc. In the embodiments illustrated these lines have been shown as rows of holes.

One row of holes can be arranged along a curve following the periphery of a cross-section of the, nozzle, the cross-section of each element marked to be shed being such that said element can pass freely through any free area concerned in the normal outlet nozzle.

Rows of holes can also be'provided along generatrices regularly distributed over the convergent body.

The time requiredfor carrying out the various stages of shedding may be preset by the constitution and disposition of the lines of preferential rupture.

Other features and advantages will become clear on reading the following description of illustrative embodiments of the self-eifacing outlet nozzle. according to the invention, with reference to the accompanying diagrammatic drawings, in which:

FIGURE 1 is a perspective diagram of a self-effacing outlet nozzle for use in the case where the normal outlet nozzle is convergent-divergent;

FIGURE la is a detail in perspective of a modification giving rise to a variant of the nozzle of FIGURE 1;

FEGURES 2 and 3 are. perspective diagrams of two further embodiments in the case where the normal outlet nozzle is convergent-divergent;

FIGURE 4 shows another embodiment with an annue lar line ofpreferential rupture, the normal outlet nozzle being solely convergent;

FIGURE 5 shows the same embodiment as in FIGURE 3, but with lines of preferential rupture following generatrices of the convergent body.

In order to simplify the drawings, the sections of the two nozzles are shown as annular in all of the figures. This condition is not restrictive as-the cross-sections can be of any suitable shape which will comply with the installation requirements for the ramjet engine on the aircraft or missile.

In FIGURE 1 the self-effacing outlet nozzle 2 is comprised by a truncated cone applied over the entire convergent portion 3 of the normal outlet nozzle 1 terminating downstream at an outlet 4 whose area of opening is smaller than that of the neck 5 of the normal outlet nozzle, and extending upstream with a short cylindrical portion 6 applied on the inner face of a cylindrical portion of the normal outlet nozzle. 1. Securing studs or bolts 7 assemble the two nozzles 1 and 2'together.

A row 8 of identical and uniformly distributed circular holes is provided around the periphery of a cross-section of the self-eifacing outlet nozzle 2 downstream of the neck 5'.

In FIGURE la, the self-effacing outlet nozzle 2 is fixed by securing bolts 7 to the normal outlet nozzle 1, as in FIGURE 1, but the latter nozzle is cylindrical adjacent either side of the interfixation between the two nozzles.

Patented May 25, 1965 "2 I .11: In FIGURE 2, the cylindrical portion shownin FIG- URE l is omitted and the upstream portion of the selfefiacing outlet nozzle 2 is no longer applied over the whole of the surface of the convergent portion 3, but only I over a portion adjacent the neck 5. The self-eifacing outlet nozzle 2 has an outlet 4. Springs 9 are uniformly distributed around the common axis x-x' of nozzles 1 and 2 downstream of the neck 5 between corresponding portions of said two nozzles, so as to hold together those portions thereof which are in contact with each other upstream of the neck 5.

A row 8 of' circular holes is provided under similar conditions to the arrangement of FIGURE 1.

The embodiment illustrated in FIGURE 3 only diifers from that of FIGURE 2 with respect to the interfixing means for the outlet nozzles 1 and 2, the springs 5? being replaced by rods 19. Each of these rods is threaded-at one of its extremities so as to be adjustably held in suitable nuts such as 11 on the self-effacing outlet nozzle 2, the other extremity of the rod bearing against the inner wall of the normal outlet nozzle.

In FIGURE 4, the normal outlet nozzle is simply convergent; The self-eifacing outlet nozzle 2 consists of a convergent body in two parts, a first frustoconical part 12 which is applied to'a corresponding portion of the truncated cone forming the convergent portion of the normal outlet nozzle 1, and a second part 13, likewise frustoconical, but which is more sharply convergent than the corresponding portion of the normal outlet nozzle and extends up to the outlet section 4 in the same plane as the outlet section 14 of the normal nozzle. Tensioned springs 9a, anchored on the self-effacing outlet nozzle 2 and bearing externally against the edge of the outlet 14, interlock the two nozzles.

A circular row of slots 15 is provided, the corresponding cross-sectional area of the inner outlet nozzle being less than that of the outlet 14 so as to allow the passage of the element shed therethrough.

It is to be noted that the outlet section 4 of the selfeffacing nozzle can be located upstream of the outlet section 14 of the normal nozzle.

The embodiment of FIGURE 5 is the same as that in FIGURE 3, the sole difference being that the annular row 8 of circular holes is replaced by rows 16 of circular holes arranged uniformly along generatrices of the truncated cone constituting the self-effacing outlet nozzle. The adjustable rods 10 enable the two nozzles 1 and 2 to be locked with respect to each other.

In all the aforesaid forms of embodiment, the selfeffacing outlet nozzle is formed of a magnesium alloy or any other alloy or material having a sufliciently low melting point. Its portion downstream of the neck. 5, or its portion 13 in the embodiment of FIGURE 4, is strongly stiffened by means of a crown 17 so as to withstand any vibrations caused by the passage of the jetstream. Its portion applied to the normal outlet nozzle must be sufficiently strong to Withstand any pressures exerted thereon.

The operation of the self-eifacing outlet nozzle is evident from the study of the drawings:

In FIGURES 1 to 3, assoon as the ramjet engine is started up hot gases cause the material to melt, firstly along the row 8 of holes, then passing through said holes to melt the dividing material therebetween, the portion of the outlet nozzle 2 downstream of said row being thereby instantaneously shed oif as a unit, shedding continuing for the remainder of said nozzle in the form of fragments and debris entrained by the exhaust gases.

In FIGURE 4 shedding takes place in exactly the same manner as in the embodiments of FIGURES 1 to 3.

In FIGURE 5 shedding takes place in a single stage since the rows 16 are positioned along the entire length of the self efiacing outlet nozzle 2. Owing to the extra thickness provided by the reinforcing crown 17, those holes which confront this crown do not have the same effect as on the remainder of the nozzle, so that the delay 4 involved in the melting-off of the whole of each element would not be consistent unless special provision is made at the crown to-this efiect, such as forming this crown or hoop in a low melting-point material and/ or increasing the number of holes thereon.

It is to 'be noted that:

The time necessary for the melting off of the nozzle 2 along the row 3 or the .row 15 of holes under the efifect of hot gases depends in particular on the shape and size of the holes, on the distance between any two adjacent holes, and on the thickness of the material. involved. Naturally, this time is also a function of the temperature of the hot gases passing through the self-etfacing outlet nozzle.

a The total time required for shedding the nozzle 2 for the embodiment shown in FIGURE 1 is longer than that for the forms of embodiment shown in FIGURES 2 to 4, or in FIGURE 5, due to the larger development of the upstream portion of said nozzle. This increase of the time required for shedding may be incompatible with good operation of the engine.

The securing bolts 7 in FIGURE 1 can in certain cases promote leakages or act as rupture initiators in the adjacent portions of the-normal outlet nozzle 1. Such dangers of leakage or rupture disappear with the use of springs 0r 9d and rods It) since thepressure inside the ramjet tendsto apply the part of the self-etfacing outlet nozzle 2 upstream of neck 5, or the part12 in the case of FIG- URE 4, against thecorresponding convergent part of the normaloutlet nozzle 1, and the interlocking of the two nozzles by the springs 9 and the rods 10 is therefore mainly eifective in centering.

It is to be understood that the present invention has merely been described and illustrated by way of explanation and Without any intention of limitation, and that various modifications can be made therein without exceeding its scope.

I claim:

1. In a ramjet including a normal outlet nozzle having at least a convergent portion,

a self-eifacing outlet nozzle comprising a convergent body whose minimum cross-section is less than the minimum cross-section of said normal outlet nozzle, said body formed of a material which melts at low temperature and mounted in said normal outlet nozzle coaxially therewith, adjacent for a portion of its length along the inner wall of the convergent portion of said normal outlet nozzle,

securing. means fixing the .two said nozzles together,

at. least one line of preferential rupture in said body of said self-effacing nozzle, comprised by a reduction in the quantity of material forming said body along said line of rupture, rupturing under the action of heat, said at least one line of preferential rupture being arranged in any suitable configuration adapted to reduce said self-effacing nozzle to a plurality of elementary portions after heating, which are shed before complete melting, thereby enabling said selfelfacing outlet nozzle to be shed in a plurality of stages,

each of said portions being smallerin overall bulk than the unobstructed area at the outlet of said normal outlet nozzle.

2. 'In the ramjet of claim 1, each said. line of preferential rupture being comprised of a row of holes, each hole being identical and uniformly spaced with respect to adjacent holes in the same row.

3. In the ramjet of claim 2, one said row of holes being located around the periphery of a cross-section of said self-efracing nozzle.

4. In the ramjet of claim 1, each ofsaid lines of preferential rupture being located along a generatrix of said self-effacing outlet nozzle.

5. In the ramjet of claim 1, said self-effacing outlet nozzle .having an outlet rim, wherein said outlet rim is reinforced by a hoop in a material which also melts at low temperature and said hoop includes weakening means, whereby said hoop is adapted to act in structurally reinforcing said self-eftacing nozzle before the ramjet is started up and in disintegrating at substantially the same rate as the remainder of said sel -effacing nozzle on being subjected to the action of heat when the ramjet is started up.

6. In the ramjet of claim 1, said securing means comprising a plurality of screws.

7. In the ramjet of claim 1, said normal outlet nozzle having a divergent portion, said securing means comprising a plurality of springs in compression between said two nozzles, said springs being attached to said selfefifacing nozzle and bearing against the inner surface of said normal nozzle, said springs being uniformly distributed around the periphery of said self-efiacing nozzle adjacent the outlet end thereof at a region downstream of the throat formed between the convergent portion and the divergent portion of said normal outlet nozzle.

8. In the ramjet of claim 1, said securing means comprising a plurality of rods, each said rod having one extrernity abutting the inner surface of said normal outlet nozzle and the other extremity being threaded and adapted to be locked at any desired penetration through the surface of said self-efiacing out-let nozzle by means of suitable nuts.

9. in the ramjet of claim 1, said securing means comprising a plurality of spring means stretched between said two nozzles, each of said spring means being anchored to said self-efiacing nozzle and adapted to hook onto the outlet edge of the convergent portion of said normal outlet nozzle.

References Cited by the Examiner UNITED STATES PATENTS 2,880,576 4/59 Kappus -35.6 2,912,820 11/59 Whitmore 6035.6 X 2,952,972 9/60 Kimmel et al.

2,984,972 5/61 Davidson 60-35.6 3,040,517 6/62 Ryden et al 6()35.6

SAMUEL LEVINE, Primary Examiner. 

1. IN A RAMJET INCLUDING A NORMAL OUTLET NOZZLE HAVING AT LEAST A CONVERGENT PORTION, A SELF-EFFECTING OUTLET NOZZLE COMPRISING A CONVERGENT BODY WHOSE MINIMUM CROSS-SECTION IS LESS THAN THE MINIMUM CROSS-SECTION OF SAID NORMAL OUTLET NOZZLE, SAID BODY FORMED OF A MATERIAL WHICH MELTS AT LOW TEMPERATURE AND MOUNTED IN SAID NORMAL OUTLET NOZZLE COAXIALLY THEREWITH, ADJACENT FOR A PORTION OF ITS LENGTH ALONG THE INNER WALL OF THE CONVERGENT PORTION OF SAID NORMAL OUTLET NOZZLE, SECURING MEANS FIXING THE TWO SAID NOZZLES TOGETHER, AT LEAST ONE LINE OF PREFERENTIAL RUPTURE IN SAID BODY OF SAID SELF-EFFACING NOZZLE, COMPRISED BY A REDUCTION IN THE QUANTITY OF MATERIAL FORMING SAID BODY ALONG SAID LINE OF RUPTURE, RUPTURING UNDER THE ACTION OF HEAT, SAID AT LEAST ONE LINE OF PREFERENTIAL RUPTURE BEING ARRANGED IN ANY SUITABLE CONFIGURATION ADAPTED TO REDUCE SAID SELF-EFFACING NOZZLE TO A PLURALITY OF ELEMENTARY PORTIONS AFTER HEATING, WHICH ARE SHED BEFORE COMPLETE MELTING, THEREBY ENABLING SAID SELFEFFACING OUTLET NOZZLE TO BE SHED IN A PLURALITY OF STAGES, EACH OF SAID PORTIONS BEING SMALLER IS OVERALL BULK THAN THE UNOBSTRUCTED AREA AT THE OUTLET OF SAID NORMAL OUTLET NOZZLE. 